Eyeground observation device and eyeground observation method

ABSTRACT

It is possible to improve the quality of an image of an eyeground, thereby acquiring an optimal image. An eyeground observation system ( 3 ) acquires an eyeground image via a compensation optical section ( 70 ) correcting the image of the eyeground obtained by illumination of an eyeground illumination system ( 2 ). A wave front correction system ( 1 ) measures wave front measurement data including a wave front aberration of the eye to be checked and/or aberration to be corrected, thereby acquiring the optical characteristic of the eye to be checked. An image data formation section ( 14 - 2 ) performs simulation of viewing at the eyeground, thereby calculating the simulation image data or MTF data. A correction amount decision section ( 14 - 3 ) decides a correction amount according to a voltage change template stored in a memory ( 144 ) and outputs it to a control section ( 15 ). Moreover, the correction amount decision section ( 14 - 3 ) uses the simulation result for a plurality of voltage change templates so as to calculate a value indicating the matching degree of the pattern or MTF data corresponding to a spatial frequency of cells of the eyeground and decide an appropriate correction amount

TECHNICAL FIELD

The present invention relates to retina observation apparatuses andretina observation methods, and more specifically, to an retinaobservation apparatus and an retina observation method that allow theaberration of an eye under examination to be corrected by means of acompensating optical device and allow observations to be made up to thecell level.

BACKGROUND ART

In the conventional retina observation, the retina of an eye underexamination has been observed with the aberration of the eye minimized.There have been disclosed a method and an apparatus of improving theeyesight and the resolution of an image on the retina by deforming anoptical correcting member like a deformable mirror (see, for example,patent document 1). In the apparatus, a Hartmann-Shack wavefront sensordetermines the wavefront aberration value of the eye, and the deformablemirror is deformed to correct the aberration value accordingly. Theprocess of deforming the deformable mirror is repeated until the RMS oferror in the determined wavefront aberration reaches the asymptoticvalue, and the deformable mirror is deformed to an appropriate shape forproviding a wavefront for correcting the aberration of the eye.

Patent Document 1

PCT International Patent Application Publication No. 2001-507258

DISCLOSURE OF INVENTION

The compensating optical device (such as the deformable mirror) wouldnot correct the aberration completely and would sometimes leave a greataberration. It is preferable that the RMS of the remaining aberration donot exceed 0.08 times the wavelength (practically no aberration). Somelow-cost compensating optical devices for a human eye may leave anaberration of about 0.2 times the wavelength. A remaining aberration ofthat level has made it difficult to improve the picture quality of theretina image. Even if the deformation of the compensating optical devicebrings the RMS of error to the level of the asymptotic value, theremaining aberration may hinder an optimum image from being obtained.

The present invention addresses the problems described above, with anobject of adjusting the correction to be made by the compensatingoptical device so that the quality of the retina image is improved andobtaining an appropriate amount of correction. Another object of thepresent invention is to obtain an appropriate amount of correction forimproving the picture quality in accordance with a value obtained frompattern matching between the manner in which a visual target isperceived by an eye under examination and a certain pattern template, oran MTF (modulation transfer function). A further object of the presentinvention is to provide an retina image corrected by an appropriatecorrection amount. A still another object of the present invention is toimprove the quality of the retina image by means of a voltage-changetemplate provided to adjust the correction amount of the compensatingoptical device. A still further object of the present invention is toevaluate the image quality in consideration of the size of the retinacell and to enable observations up to the cell level.

According to a first solving means of this invention, there is provided

an retina observation apparatus comprising:

an retina illumination unit for illuminating the retina of an eye underexamination for the purpose of observation;

a compensating optical section for correcting a image of the retinaformed by the illumination of the retina illumination unit by a givenamount of correction;

an retina-image-forming optical block for forming an retina image byreceiving the image of the retina corrected by the compensating opticalsection;

an retina-image-light-receiving section for receiving the retina imageformed by the retina-image-forming optical block;

a wavefront measurement block for obtaining wavefront measurement dataincluding at least either or both of a wavefront aberration of the eyeunder examination and the aberration corrected by the compensatingoptical section;

an optical characteristics measurement block for obtaining opticalcharacteristics including a high-order aberration of the eye underexamination, from the wavefront measurement data given by the wavefrontmeasurement block;

an image data formation block for simulating the manner in which avisual target is perceived on the retina, in accordance with the opticalcharacteristics obtained by the optical characteristics measurementblock, and calculating data indicating the manner of perception;

a storage block for storing a plurality of voltage-change templates foruse in an adjustment of the compensating optical section; and

a correction amount determination block for selecting a voltage-changetemplate stored in the storage block, determining an amount ofcorrection to be made by the compensating optical section in accordancewith the template and outputting the amount of correction to thecompensating optical section, obtaining evaluation data for evaluatingthe quality of the image in accordance with the data indicating themanner in which the visual target is perceived, obtained by the imagedata formation block, in consideration of the amount of correction basedon the plurality of voltage-change templates, determining an appropriateamount of correction to be made by the compensating optical section inaccordance with the evaluation data, and outputting the appropriateamount of correction to the compensating optical section.

According to a second solving means of this invention, there is provided

an retina observation method comprising:

a step of illuminating the retina of an eye under examination for thepurpose of observation;

a step of correcting a image of the retina formed by the illumination,by a given amount of correction;

a step of forming an retina image by receiving the corrected image ofthe retina;

a step of measuring wavefront measurement data indicating at leasteither or both of a wavefront aberration of the eye under examinationand the aberration to be corrected;

a step of obtaining optical characteristics including a high-orderaberration of the eye under examination, from the wavefront measurementdata;

a step of calculating data indicating the manner of perception, bysimulating the manner in which a image is perceived on the retina, inaccordance with the obtained optical characteristics;

a step of determining and outputting the amount of correction inaccordance with the template which is selected a voltage-change templatefor use in an adjustment of an amount of correction and;

a step of determining an appropriate amount of correction in accordancewith the evaluation data which is obtained for evaluating the quality ofthe image in accordance with the data indicating the manner in which theimage is perceived, in consideration of the amount of correction basedon a plurality of voltage-change templates and

a step of outputting the amount of correction determined in the step ofdeterming.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the configuration of an retina observationapparatus.

FIG. 2 is a view showing the configuration of a deformable mirror.

FIG. 3 shows the format of a reference voltage table for storing areference voltage of a voltage change.

FIG. 4 shows the format of a table of concentric templates.

FIG. 5 shows the format of a table of symmetric templates.

FIG. 6 shows the format of a table of asymmetric templates.

FIG. 7 shows a format of template matching, including matching values.

FIG. 8 shows a flow chart for retina observation.

FIG. 9 shows a flow chart for selecting a voltage-change template.

FIG. 10 is a view illustrating the best judgment in accordance withvariations in MTF.

FIG. 11 shows a flow chart for MTF optimization.

FIG. 12 is a view showing the relationship between the distance from amacular and the spatial frequency of a cell.

FIG. 13 shows a flow chart for MTF(cf) calculation.

FIG. 14 shows a flow chart for pattern optimization.

FIG. 15 shows a flow chart for calculation of pattern matching valueP_(k).

FIG. 16 is a view showing the relationship between the distance from themacular and a cell size.

FIG. 17 is a view illustrating pattern original images.

FIG. 18 is a view illustrating pattern template images PT(x,y).

FIG. 19 is a view comparing an image obtained through patternoptimization with other images.

BEST MODE FOR CARRYING OUT THE INVENTION

1. Hardware Configuration

FIG. 1 is a diagram showing the configuration of an retina observationapparatus. The retina observation apparatus includes a wavefrontcorrection unit 1, an retina illumination unit 2, an retina observationunit 3, an alignment unit 4, a fixation unit 5, and a compensatingoptical section 70. The wavefront correction unit 1 includes apoint-image-projecting optical block 11, a point-image-light-receivingoptical block 12, a wavefront measurement block 10 containing apoint-image-light-receiving section 13, a computer 14, and a controlblock 15. The retina observation unit 3 includes an retina-image-formingoptical block 31 and an retina-image-light-receiving section 32. Thecomputer 14 includes an optical characteristics measurement block 14-1,an image data formation block 14-2, a compensation amount determinationblock 14-3, and a memory 14-4. The computer 14 may also include adisplay block 14-5, an input block, and the like. The figure shows theretina (retina) 61 and the cornea (anterior) 62 of an eye underexamination 60.

The first illumination optical block (point-image-projecting opticalblock) 11 contains, for example, a first light source, and illuminates aminute area on the retina of the eye under examination with a light beamfrom the first light source. The first illumination optical system 11also contains a condenser lens and a relay lens, for instance.

It is preferable that the first light source have a high spatialcoherence and a low time coherence. The first light source in thisembodiment is a super luminescence diode (SLD), which provides ahigh-intensity point light source. The first light source is notnecessarily the SLD, and a device having a high spatial coherence and ahigh time coherence, such as a laser device, can also be used if thetime coherence is appropriately lowered by inserting a rotating diffuseror the like. A device not having a high spatial coherence nor having ahigh time coherence, such as an LED, can be used by providing a pinholeor the like in the position of the light source in the optical path, ifthe amount of light is sufficient. The first wavelength of the firstlight source for illumination can be an infrared wavelength of 780 nm,for instance.

The first light-receiving optical block (point-image-light-receivingoptical block) 12 receives a light beam reflected back from the retinaof an eye under examination and guides the light beam to the firstlight-receiving section (point-image-light-receiving section) 13. Thefirst light-receiving optical block 12 includes a relay lens, a beamsplitter, and a conversion member (splitting element) for converting areflected light beam to at least seventeen beams. The beam splitterincludes a mirror (polarizing beam splitter, for instance) forreflecting the light beam coming from the first light source and passingthe light beam which has been returning through an afocal lens 81 afterbeing reflected by the retina of the eye under examination 60. Theconversion member is a wavefront conversion member for converting thereflected light beam to a plurality of beams. The conversion member canbe a plurality of micro-Fresnel lenses disposed in a plane orthogonal tothe optical axis. The light reflected from the retina 61 is gatheredthrough the conversion member onto the first light-receiving section 13.

The first light-receiving section 13 receives light from the firstlight-receiving optical block 12 through the conversion member andgenerates a first signal. The front focal point of the afocal lens 81approximately agrees with the pupil of the eye under examination 60.

The first illumination optical block 11 and the first light-receivingoptical block 12 keep such a relationship that the peak of the signalgenerated from the reflected light by the first light-receiving section13 is maximized, on the assumption that the light is reflected at apoint where light beams from the first light source gather, and a prism72 can move in such a direction that the peak of the signal generated bythe first light-receiving section 13 increases and can stop in aposition where the intensity is maximized. As a result, the light beamfrom the first light source gathers onto the eye under examination.

The second illumination optical unit (retina illumination unit) 2includes, for example, a second light source, a condenser lens, and abeam splitter, and illuminates a certain region on the retina of the eyeunder examination with a second light beam coming from the second lightsource. The second light source emits a red light beam having a secondwavelength of 630 nm, for instance. The second light source is a pointlight source or an area light source for the retina 61 and can be in thered region. The wavelength can be appropriately selected: for instance,the first light source for Hartmann measurement has a wavelength of 840nm, and the light source for lighting the anterior, not shown, haswavelengths of 850 to 930 nm (860 to 880 nm at present) in the infraredor near-infrared region. The beam splitter can be a polarizing beamsplitter for reflecting a light beam coming from the second light sourceand passing a light beam reflected back from the eye under examination60.

Illumination on the retina 61 may be provided by a mirror with anopening, for instance, and may be limited to the observation area of theretina 61. The mirror with an opening and the pupil should conjugate toavoid reflection at the top of the cornea. Alternatively, a ring-shapedaperture having 100% transmittance at the center and 10% transmittancein the periphery, for instance, may be used to illuminate the whole ofthe retina 61.

The second light-receiving optical block (retina-image-forming opticalblock) 31 includes, for instance, the afocal lens 81, the compensatingoptical section 70, a beam splitter, and a condenser lens. The secondlight-receiving optical block guides light with a second wavelengthreflected by the retina 61, through the compensating optical section 70to the second light-receiving section (retina-image-light-receivingsection) 32. The beam splitter includes, for instance, a dichroic mirrorwhich reflects a light beam with the first wavelength and passes a lightbeam with the second wavelength. The second light-receiving section 32receives the retina image formed by the second light-receiving opticalblock 31 and generates a second signal. The second light-receivingsection 32 can also be formed by a light-receiving element having asensitivity to the second wavelength (red light).

The compensating optical section 70 includes a compensating opticaldevice 71 such as adaptive optics for compensating for aberration ofmeasured light and either or both of a spherical lens and a moving prism72 for correcting a spherical component while moving in the direction ofthe optical axis. The compensating optical section 70 is disposed in thefirst light-receiving optical block 12 and the second light-receivingoptical block 31 and compensates for aberration of a light beamreflected from the eye under examination 60. The compensating opticalsection 70 may also compensate for aberration of the light beam emittedfrom the first light source, so that a minute area on the retina of aneye under examination can be illuminated by the aberration-compensatedlight beam.

As the compensating optical device 71, a deformable mirror, aliquid-crystal spatial optical modulator, or the like can be used.Another appropriate optical system that can compensate for aberration ofmeasured light may also be used. The deformable mirror reflects a lightbeam at an angle depending on how the mirror is deformed by an internalactuator. The deformation may be caused by a capacitance, a piezoeffect, or any other appropriate factor. The liquid-crystal spatialoptical modulator modulates the phase, by making use of the lightdistribution property of the liquid crystal, and reflects light like amirror. The liquid-crystal spatial optical modulator may sometimesrequire a polarizer to be placed in the middle of the optical path. Thecompensating optical device 71 may not be a reflecting element but atransmitting optical element. The compensating optical device 71compensates for aberration by deformation, for instance, depending onthe output from the control block 15.

The light beams entering the compensating optical device 71 arepreferably, but not limited to be, parallel. If the eye underexamination 60 has no aberration, for instance, light beams reflected bythe retina of the eye under examination 60 enter the compensatingoptical device 71 as parallel light beams. The light beams coming fromthe first light source also enter the compensating optical device 71 asparallel light beams.

The moving prism 72 moves in the direction of the optical axis inaccordance with the output from the computer 14. The moving prism 72 isdriven, for instance, by an appropriate driving section. The movement ofthe moving prism 72 allows a spherical component to be compensated for.The compensation can be obtained by using a spherical lens insteadmoving the moving prism 72.

The alignment unit 4 includes a condenser lens and an alignmentlight-receiving block. The alignment unit 4 guides light beams emittedfrom a light source and reflected from the cornea 62 of the eye underexamination 60 to the alignment light-receiving block. The alignmentunit may have an alignment light source or may use an appropriate lightsource for illuminating the eye under examination 60. In addition, whena certain pattern (such as a Placido ring) is projected by an opticalsystem, not shown, the alignment unit 4 can guide light beams reflectedfrom the anterior or cornea 62 of the eye under examination 60 to thealignment light-receiving block. The alignment light-receiving block canobtain an anterior image. In comparison with the first wavelength (780nm in this embodiment), a long wavelength (940 nm, for instance) can beselected for the light beams used for alignment.

The third illumination unit (fixation unit) 5 contains an optical pathto throw a visual target for the purpose of fixation or fogging of theeye under examination 60, and includes a third light source 51 (lamp,for instance), a fixation target 52, and a relay lens. The light beamscoming from the third light source 51 allow the fixation target to bethrown onto the retina 61, and the eye under examination 60 can observethe image.

The optical characteristics measurement block 14-1 of the computer 14obtains the optical characteristics including high-order aberrations ofthe eye under examination 60, in accordance with the output from thefirst light-receiving section 13. The optical characteristicsmeasurement block 14-1 may obtain the optical characteristics from atleast wavefront measurement data indicating the wavefront aberration ofthe eye under examination 60 as well as the output from the firstlight-receiving section 13.

The image data formation block 14-2 simulates the manner in which thevisual target is perceived, in accordance with the opticalcharacteristics, and calculates simulated image data or thecharacteristic data of the eye under examination such as an MTFindicating the manner of perception.

The memory 14-4 stores a plurality of voltage-change templates for usein an adjustment of the compensating optical device.

The correction amount determination block 14-3 selects onevoltage-change template stored in the memory 14-4, determines acorrection amount of the compensating optical device in accordance withthe selected template, and outputs the correction amount to the controlblock 15. The correction amount determination block also obtainsevaluation data for evaluating the quality of the retina image, on thebasis of the characteristic data of the eye under examination or thesimulated image data obtained for the plurality of voltage-changetemplates, and determines an appropriate correction amount of thecompensating optical element in accordance with the evaluation data. Avalue indicating the degree of matching between a simulated image and acertain pattern template or an MTF can be used, for instance, as theevaluation data.

The control block 15 deforms the deformable mirror 71 in accordance withthe output from the computer 14. The control block 15 also moves themoving prism 72 in the direction of the optical axis in accordance withthe output from the computer 14. The movement of the moving prism 72allows a spherical component to be corrected.

(Conjugation)

The retina 61 of the eye under examination 60, the fixation target 52 ofthe fixation unit 5, the first light source, and the firstlight-receiving section 13 conjugate. The pupil (iris) of the eye underexamination 60 and the conversion member (Hartmann plate) of the firstlight-receiving optical block 12 conjugate. The second light sourceconjugates the pupil (an image is formed on the pupil) and canilluminate the most of the retina 61 evenly.

(Alignment Adjustment)

An alignment adjustment will next be described. An alignment adjustmentis made mainly by the alignment unit 4.

Light beams from a light source pass through a condenser lens, a beamsplitter, and the afocal lens 81, and the parallel light beamsilluminate the eye under examination 60. The light beams reflected bythe cornea 62 of the eye under examination 60 are returned as if theywere diverging from a point positioned at half the radius of curvatureof the cornea 62. The diverging light beams pass through the afocal lens81, the beam splitter, and the condenser lens, and the alignmentlight-receiving block receives the light beams as a spot image.

If the spot image on the alignment light-receiving block is not on theoptical axis, the retina observation apparatus is moved up and down andside to side so that the spot image comes on the optical axis. When thespot image is brought onto the optical axis, an alignment adjustment iscompleted. A light source, which is not shown, for illuminating thecornea 62 of the eye under examination 60 forms an image of the eyeunder examination 60 on the alignment light-receiving block. This imagemay also be used in an alignment adjustment to align the center of thepupil with the optical axis.

(Compensating Optical Device 71)

FIG. 2 is a view showing the configuration of the compensating opticaldevice 71. If a deformable mirror having a neatly arranged group ofelements is used, the deformable mirror is deformed by the movement ofeach element caused by its actuator. Each element is assigned beforehandan element number for identifying the element. The control block 15drives each element by means of the corresponding actuator in accordancewith a voltage value for the corresponding element number output by thecomputer 14. The number of elements is not limited to the number shownin the figure and can be any appropriated number. Element numbers notshown in the figure can be assigned. Besides the element numbers, text,coordinates, and any other appropriate identification information thatcan identify each element can be used.

FIG. 3 shows the format of a reference voltage table for storing areference voltage of a voltage change. A reference voltage for changingthe voltage applied to the element is stored in association with eachelement number of the compensating optical device 71. The computer 14determines a voltage value to be applied to the compensating opticaldevice 71 in accordance with the reference voltage stored here and avoltage change given by a voltage-change template, which will bedescribed later, and outputs the value to the control block 15. Thereference voltage table stores, for instance, a value of the voltageapplied to the compensating optical device 71 before the correctionamount is adjusted in accordance with the voltage change template. Thecomputer 14 also updates the voltage value to a new value after thecorrection amount adjustment.

FIG. 4 shows the format of a table of concentric templates. The table ofFIG. 4 shows that nine templates are stored for the compensating opticaldevice 71 having 37 elements. Each template stores a value of voltagechange corresponding to an element number. Generally speaking, elementsnear the center of the compensating optical device 71 have great effectson the picture quality, so that larger voltage changes can be specifiedinside in the concentric templates. This embodiment has a template withall voltage changes specified to zero. This template makes it possibleto compare evaluation data without voltage change and evaluation datawith voltage changes, for instance.

FIG. 5 shows the format of a table of symmetric templates. Each templatestores values of voltage change in association with element numbers. Inthe symmetric template, symmetric values of voltage change can bespecified about the center of the compensating optical device 71. Thesymmetric template may also have symmetric values of voltage changeabout the x axis, the y axis, or any other axis.

FIG. 6 shows the format of a table of asymmetric templates. Eachtemplate stores values of voltage change in association with elementnumbers. In the asymmetric template, asymmetric values of voltage changecan be specified about the center or an axis.

The number of templates and the number of elements are not necessarilythe numbers shown in FIGS. 4 to 6, and any number of templates orelements can be included. A required value of voltage change can bespecified.

FIG. 7 shows a format of template matching, including matching values. Amatching value obtained by template matching, which will be describedlater, a value of voltage applied to each element of the compensatingoptical device 71 used for the measurement, and a template number arestored in association with one another. MTF and other data may be storedinstead of the matching value, in association with a template number.The value of voltage applied to each element may be omitted. In thatcase, the computer 14 can calculate the value of voltage applied to eachelement of the compensating optical device 71, with reference to thereference voltage table and a voltage-change template having thecorresponding template number.

2. Zernike Analysis

Next, a Zernike analysis will be described. A generally known method ofcalculating Zernike coefficients C_(i) ^(2j−i) from Zernike polynomialswill be described. The Zernike coefficients C_(i) ^(2j−i) are importantparameters for grasping the optical characteristic of the subject eye 60on the basis of inclination angles of the light fluxes obtained by thefirst light receiving part 13 through the conversion member, for exampleHartmann plate.

Wavefront aberrations W(X, Y) of the subject eye 60 are expressed usingthe Zernike coefficients C_(i) ^(2j−i) and the Zernike polynomials Z_(i)^(2j−i) by the following expression.${W\left( {X,Y} \right)} = {\sum\limits_{i = 0}^{n}{\sum\limits_{j = 0}^{i}{c_{i}^{{2j} - i}{Z_{i}^{{2j} - i}\left( {X,Y} \right)}}}}$

Where, (X, Y) denotes vertical and horizontal coordinates of theHartmann plate.

Besides, with respect to the wavefront aberrations W(X, Y), when thehorizontal and vertical coordinates of the first light receiving part 13are denoted by (x, y), a distance between the Hartmann plate and thefirst light receiving part 13 is denoted by f, and a movement distanceof a point image received by the first light receiving part 13 isdenoted by (Δx, Δy), the following expression is established.$\frac{\partial{W\left( {X,Y} \right)}}{\partial X} = \frac{\Delta\quad x}{f}$$\frac{\partial{W\left( {X,Y} \right)}}{\partial Y} = \frac{\Delta\quad y}{f}$

Where, the Zernike polynomials Z_(i) ^(2j−i) are expressed by thefollowing numerical expressions. (More specifically expressions, forexample, see JP-A-2002-209854.)$Z_{n}^{m} = {{R_{n}^{m}(r)}\left\{ \frac{\sin}{\cos} \right\}\left\{ {m\quad\theta} \right\}}$$\begin{matrix}{m > 0} & \sin \\{m \leqq 0} & \cos\end{matrix}$${R_{n}^{m}(r)} = {\sum\limits_{S = 0}^{{({n - m})}/2}{\left( {- 1} \right)^{S}\frac{\left( {n - S} \right)!}{{S!}{\left\{ {{\frac{1}{2}\left( {n - m} \right)} - S} \right\}!}{\left\{ {{\frac{1}{2}\left( {n + m} \right)} - S} \right\}!}}r^{m}}}$

Incidentally, with respect to the Zernike coefficients C_(i) ^(2j−i),specific values can be obtained by minimizing the squared errorexpressed by the following numerical expression.${S(x)} = {\sum\limits_{i = 1}^{{data}\quad{number}}\left\lbrack {\left\{ {\frac{\partial{W\left( {X_{i},Y_{i}} \right)}}{\partial X} - \frac{\Delta\quad x_{i}}{f}} \right\}^{2} + \left\{ {\frac{\partial{W\left( {X_{i},Y_{i}} \right)}}{\partial Y} - \frac{\Delta\quad y_{i}}{f}} \right\}^{2}} \right\rbrack}$

Where, W(X, Y): wavefront aberrations, (X, Y): Hartmann platecoordinates, (Δx, Δy): a movement distance of a point image received bythe first light receiving part 13, f: a distance between the Hartmannplate and the first light receiving part 13.

The computer 14 calculates the Zernike coefficients C_(i) ^(2j−i), anduses this to obtain eye optical characteristics such as sphericalaberrations, coma aberrations, and astigmatism aberrations. The computer14 calculates aberration quantities RMS_(i) ^(2j−i) using the Zernikecoefficients C_(i) ^(2j−i) by the following numerical expression.${RMS}_{i}^{{2j} - i} = {\sqrt{\frac{ɛ_{i}^{{2j} - i}}{2\left( {i + 1} \right)}}{c_{i}^{{2j} - i}\left( {{ɛ_{i}^{{2j} - i} = {2\left( {{2j} = i} \right)}},\quad{ɛ_{i}^{{2j} - i} = {1\left( {{2j} \neq i} \right)}}} \right)}}$3. Flow Charts

FIG. 8 shows a flow chart for retina observation. The retina observationapparatus first performs alignment of the eye under examination 60(S101).

The computer 14 (arithmetic logical unit, for instance) specifies amacular as an origin and a position where the optical axis from thefirst light source meets the retina 61 as (X_(re), Y_(re)) (S103). Thecomputer 14 can obtain, for instance, an retina image from the secondlight-receiving section and can detect the positions of the macular andthe point where the optical axis meets the retina 61 through imageprocessing. The position of the macular can be detected, for example, bya normalized correlation method, with reference to a macular templatecreated and stored beforehand in the memory. The computer 14 may alsodisplay an obtained image on the display block and may allow theoperator of the retina observation apparatus to specify the positions ofthe macular and the point where the optical axis meets the retina 61 byusing a pointing device or another appropriate input device.

The computer 14 then measures wavefront aberration of the eye underexamination 60 in accordance with the signal from the firstlight-receiving section 13 (S105). The computer 14 judges whether themeasured aberration is smaller than a predetermined threshold (S107).The computer 14 can, for instance, calculate an aberration amountRMS_(i) ^(2j−i) from the Zernike coefficient C_(i) ^(2j−i) obtained instep S105 and judge whether the aberration amount RMS is smaller thanthe threshold.

If the aberration exceeds the threshold (S107), the computer 14 deformsthe deformable mirror 71 to cancel out the aberration in accordance withthe measured wavefront aberration (wavefront data) (S109). For example,the computer 14 determines a value of voltage applied to each element ofthe compensating optical device 71 in accordance with the measuredwavefront aberration, and outputs the determined value of voltage to thecontrol block 15. The computer 14 also stores the output voltage valuein association with the element number in the reference voltage tableprovided in the memory. The computer 14 then returns to the processingof step S105.

If the aberration amount RMS is smaller than the threshold (S107), thecomputer 14 initializes flags (S111). For instance, the computer 14resets flags A, B, and C to zero. The flags will be described in furtherdetail with another flow chart.

The computer 14 next selects a voltage-change template (S113). Forinstance, the computer 14 selects a concentric template, a symmetrictemplate, or an asymmetric template, in accordance with either or bothof the flags and the aberration amount. The selection of a template willbe described later in further detail.

The computer 14 checks whether flag C is 2 (S115). If flag C is not 2(S115), the computer 14 performs MTF optimization or patternoptimization (S117). The computer 14 changes the value of voltageapplied to the deformable mirror 71 in accordance with thevoltage-change template selected in step S113, and obtains a value ofvoltage V_(i) that maximizes MTF or the matching value of the simulatedretina image of a certain pattern and a pattern template. The MTFoptimization and pattern optimization will be described later in furtherdetail.

The computer 14 outputs the value of voltage V_(i) obtained in step S117to the deformable mirror 71 (S119). The computer 14 measures wavefrontaberration after a certain period of time has passed since the voltagevalue is output, in consideration of a period of deformation of thedeformable mirror 71. The computer 14 may read wavefront data measuredand stored in association with the value of voltage V_(i) from thememory, instead of measuring wavefront aberration. The computer 14 thenreturns to the processing of step S113, selects a voltage-changetemplate, and repeats the processing of step S115 and below.

If it is found that flag C is 2 in step S115, the computer 14 obtains anretina image from the second light-receiving section 32 (S121). Thecomputer 14 stores the obtained retina image in the memory (S123) andends the processing.

FIG. 9 shows a flow chart for selecting a voltage-change template.

The computer 14 first specifies a threshold “th” of the RMS value as acondition for a branch (S201). The computer 14 sets the value of thethreshold “th” to a very small value of aberration (such as 0.1). Thecomputer 14 calculates Zernike coefficient c_(i) ^(2j−i) from theaberration and converts the coefficient to an aberration amount R_(i)^(2j−i) (S203). The aberration amount R_(i) ^(2j−i) can be obtained bythe following expression:$R_{i}^{{2j} - i} = {\frac{ɛ_{i}^{{2j} - i}}{2\left( {i + 1} \right)}\left( c_{i}^{{2j} - i} \right)^{2}}$(ɛ_(i)^(2j − i) = 2(2j = i),  ɛ_(i)^(2j − i) = 1(2j ≠ i))The computer 14 may also use the RMS obtained by expression 6 instead ofthe expression indicated above, as R_(i) ^(2j−i).

The computer 14 checks whether flag A is 1 (S205). If flag A is 1(S205), the computer 14 goes to step S213. If flag A is not 1 (S205),the computer 14 checks whether the total amount of spherical aberrationsR₂ ⁻², R₄ ⁻⁴, R₆ ⁻⁶, exceeds the threshold “th” (S207). If Yes in stepS207, the computer 14 specifies a concentric template as avoltage-change template (S209). The computer 14 also sets flag A to 1(S211), completes the selection of the voltage-change template, and goesto step S115 in FIG. 8. If No in step S207, the computer 14 returns tothe processing of step S215.

The computer 14 checks whether flag B is 1 (S213). If flag B is 1(S213), the computer goes to step S221. If flag B is not 1 (S213), thecomputer goes to step S215.

The computer 14 checks whether the total amount of R_(i) ^(2j−i) (i isan even number, and j is not zero) corresponding to the astigmaticcomponent exceeds the threshold “th” (S215). If Yes in step S215, thecomputer 14 specifies a symmetric template as a voltage-change template(S217). The computer 14 also sets flag B to 1 (S219) and completes theselection of the voltage-change template. If No in step S215, thecomputer 14 goes to step S221.

The computer checks whether flag C is 1 (S221). If flag C is 1 (S221),the computer 14 goes to step S229. If flag C is not 1 (S221), thecomputer 14 checks whether the total amount of R_(i) ^(2j−i) (i is anodd number) corresponding to a coma-like aberration component exceedsthe threshold “th” (S223). If Yes in step S223, the computer 14specifies an asymmetric template as a voltage-change template (S225).The computer 14 also sets flag C to 1 (S227) and completes the selectionof the voltage-change template.

If No in step S223 or if it is found in step S221 that flag C is 1, thecomputer 14 sets flag C to 2 (S229) and completes the selection of thevoltage-change template.

(MTF Optimization)

FIG. 10 is a view illustrating the determination of an optimum image inaccordance with variations in MTF. With MTF, the degree of resolvingpower at a certain level of fineness can be checked. The figure shows agraph plotted when the deformable mirror 71 is deformed as representedby lines A and B, with the vertical axis representing the MTF value usedas a measure of resolving power and the horizontal axis representing thespatial frequency used as a measure of fineness. The unit of the spatialfrequency is lines/mm or cycles/degree in most cases.

The graph shows that the RMS value of B is smaller than that of A andthat the MTF value of B is higher than that of A while the spatialfrequency is up to 400 lines/mm. If an image close to the diffractionlimit is required as with adaptive optics, A showing a resolving powerin the high-frequency region above 400 lines/mm is more preferable to B.

In this embodiment, when some different voltages are applied to deformthe deformable mirror 71 in accordance with the voltage-change template,the MTF value at 500 lines/mm (value for resolving an object ofapproximately 2 μm) is calculated. By selecting a value of voltage thatmaximizes the calculated MTF, a small image can be observed.

FIG. 11 shows a flow chart for MTF optimization.

The computer 14 calculates the distance between the position (X_(re),Y_(re)) where the optical axis of light illuminating the retina 61 ofthe eye under examination 60 meets the retina 61 and the macular (originof the coordinate system), and obtains the spatial frequency cfcorresponding to the calculated distance with reference to the table ofthe spatial frequency of the cell (S301).

FIG. 12 is a view showing the relationship between the distance from themacular and the spatial frequency of the cell. For the human eye, thespatial frequency of the cell decreases as the distance from the macularincreases, as shown in FIG. 12. The shown relationship may be stored inthe memory as a table indicating the relationship between the distancefrom the macular and the spatial frequency, so that the computer 14 canread the spatial frequency cf corresponding the calculated distance fromthe memory. Alternatively, an approximate expression representing therelationship between the distance from the macular and the spatialfrequency as shown in FIG. 12 may be stored in the memory, so that thecomputer 14 can calculate the spatial frequency cf corresponding to thecalculated distance in accordance with the approximate expression.

Then, the computer 14 specifies the initial voltage as V (Vi: i=1 to n),where n is the number of elements of the deformable mirror 71 (S303).The computer 14 can read the voltage corresponding to each elementnumber from the reference voltage table stored in the memory and canspecify this voltage as the initial voltage V.

The computer 14 specifies a template number k to 1, for instance (S305).The template number functions as a counter for calculating the MTF of aplurality of templates.

The computer 14 reads the voltage-change template selected in step S113as v^((k)) from the memory (S307). The computer 14 reads all thetemplates stored in the memory, for example, each voltage-change amountof template number 1 as v⁽¹⁾ each voltage-change amount of templatenumber 2 as v⁽²⁾ and so on. The computer 14 also reads the templatecount m from the memory. The computer 14 may count the number of readtemplates and specify it as a template count m, instead of reading thetemplate count.

The computer 14 specifies voltage value T_(i) (S309), as expressed by:T _(i) =V _(i) +v _(i) ^((k))(i=1 to n)The computer 14 changes the value of the voltage to be applied to eachelement of the deformable mirror 71 to T_(i), and outputs T_(i) to thecontrol block 15 (S311). The control block 15 deforms the deformablemirror 71 by driving each element of the deformable mirror 71 inaccordance with the voltage T_(i) output from the computer 14. Thecomputer 14 measures wavefront aberration W(x,y) after the deformablemirror 71 is deformed (after a certain period of time, for instance)(S313).

The computer 14 calculates MTF(cf) from the measured wavefrontaberration (S315). MTF(cf) is an average of MTFs at all anglescorresponding to the spatial frequency cf of the cell, for instance. Thecalculation of MTF(cf) will be described later. The computer 14 sets thecalculated MTF(cf) as M_(k) (S317). The computer 14 also stores M_(k) inthe memory in association with the template number k. The computer 14may store the measured wavefront aberration, data based on theaberration, and the voltage T_(i) at a certain timing, in associationwith the template number k.

The computer 14 checks whether the template number k is smaller than thetemplate count m (S319). That is, the computer 14 checks whether M_(k)has been obtained for all the templates. If the template number k issmaller than the template count m (S319), the computer 14 increments kby one (S321) and repeats the processing of step S309 and below.

If the template number k is greater than template count m (S319), thecomputer 14 substitutes the value of k that maximizes M_(k) (k=1 to m)for “a” (S323). For instance, the computer 14 searches for M_(k) havinga greater value than any other M_(k) stored in the memory, reads thecorresponding template number k, and substitutes this “k” for “a”.

The computer specifies the voltage V_(i) obtained by the followingexpression (S325):V _(i) =V _(i) +v _(i) ^((a))(i=1 to n)The computer 14 enters the specified V_(i) in the reference voltagetable stored in the memory. If voltages corresponding to M_(k) havealready been stored in the memory, the computer 14 may search for M_(k)having a greater value than any other M_(k) stored in the memory, readthe voltage corresponding to this M_(k), and specify the voltage asV_(i) in step S323. Then, the processing of step S325 can be omitted.The computer 14 then terminates the MTF optimization and goes to stepS119 in FIG. 8. The processing described above specifies the voltageV_(i) to maximize MTF(cf).

FIG. 13 shows a flow chart for MTF(cf) calculation.

The computer 14 obtains pupil function f(x,y) from wavefront aberrationW(x,y), as indicated below (S401):f(x,y)=e ^(ikw(x,y))

(i: Imaginary, k: Wave vector (2π/λ), λ: Wavelength) The computer thencalculates spatial frequency distribution OTF(u,v) of the eye inaccordance with the pupil function (S403). The calculation of thespatial frequency distribution of the eye is described below.

The computer 14 first obtains a point spread function by amplitudeU(u,v), through a Fourier transform of pupil function (x,y), asexpressed below: $\begin{matrix}{{U\left( {u,v} \right)} = {\int{\int_{- \infty}^{\infty}{{f\left( {x,y} \right)}{\exp\left\lbrack {{- \frac{\mathbb{i}}{R}}\frac{2\pi}{\lambda}\left( {{ux} + {vy}} \right)} \right\rbrack}{\mathbb{d}x}{\mathbb{d}y}}}}} & \quad\end{matrix}$

-   (λ: Wavelength,-   R: Distance from pupil to image point (retina),-   (u,v): Coordinates in a plane orthogonal to the optical axis, with    reference to image point O set to origin,    (x,y): Coordinates in pupil plane)    The computer 14 multiplies U(u,v) by its complex conjugate number    and obtains I(u,v), a point spread function (PSF), from the    following expression:    I(u,v)=U(u,v)U*(u,v)    The computer 14 obtains OTF by normalizing PSF by means of a Fourier    transform (or self-correlation) as expressed below:    R(r, s) = ∫∫_(−∞)^(∞)I(u, v)𝕖^(−𝕚2π(ru + sv))𝕕u𝕕v(r, s:  Variables  in  spatial  frequency  domain)    ${OTF} = \frac{R\left( {r,s} \right)}{R\left( {0,0} \right)}$

The computer 14 obtains MTF(u,v) from OTF(u,v) as expressed below(S405):MTF(u,v)=|OTF(u,v)|The computer initializes parameters (S407). For instance, the computerspecifies angle θ to 0° and ALLMTF, or the sum of MTF, to 0, andspecifies a partition number “d” to a certain value (36, for instance).The partition number “d” represents the number of partitions into whichan angle of 180° is divided in MTF calculation. If “d” is set to 36,angle θ can be specified in units of 5°. Any value can be specified as“d”, but a multiple of 2 is preferable.

The computer 14 calculates v and v in accordance with the followingexpressions (S409):u=cf×cos(θ)v=cf×sin(θ)where cf is the spatial frequency obtained in step S301.

The computer 14 obtains MTF(u,v) in accordance with u and v calculatedabove and obtains ALLMTF in accordance with the following (S411):ALLMTF=ALLMTF+MTF(u,v)The computer 14 then changes the angle θ in accordance with thefollowing expression (S413):θ=θ+180/d

The computer 14 checks whether θ is greater than 180° (S415). If θ issmaller than 180° (S415), the computer 14 returns to step S409. If θ isgreater than 180° (S415), the computer 14 calculates MTF(cf) inaccordance with the following expression (S417):MTF(cf)=ALLMTF/dThe computer than terminates the MTF(cf) calculation and goes to stepS317 in FIG. 11.(Pattern Optimization)

FIG. 14 shows a flow chart for pattern optimization.

The computer 14 performs steps S303 to S313. Those steps have beendescribed above, and detailed descriptions thereof will not be repeatedbelow. The computer 14 calculates a pattern matching value P_(k) (S515).The computer 14 simulates a retina image of a certain pattern, comparesa pattern template corresponding to the pattern and the simulated retinaimage through pattern matching, and obtains the pattern matching valueP_(k). The specific method of obtaining the pattern matching value P_(k)will be described later. The computer 14 stores the calculated patternmatching value P_(k) in association with both or either of the templatenumber k and voltage V_(i) in the memory (S517).

The computer 14 then checks whether the template number k is smallerthan the template count m (S319). If the template number k is smallerthan the template count m (S319), the computer 14 increments k by one(S321) and repeats the processing of step S309 and below. If thetemplate number k is greater than the template count m (S319), thecomputer 14 substitutes the value of k that maximizes P_(k) (k=1 to m)for “a” (S523). For instance, the computer 14 searches for P_(k) havinga greater value than any other P_(k) stored in the memory, reads thecorresponding template number k, and substitutes “k” for “a” Thecomputer 14 performs step S325, specifies the voltage V_(i), and addsV_(i) to the reference voltage table stored in the memory. If voltagescorresponding to P_(k) have already been stored in the memory, thecomputer 14 may search for P_(k) having a greater value than any otherP_(k) stored in the memory, read the value of voltage corresponding tothis P_(k), and specify the value as V_(i) in step S523. Then, theprocessing of step S325 can be omitted. Now, the voltage V_(i) thatmaximizes pattern matching value P_(k) is specified.

FIG. 15 shows a flow chart for calculation of pattern matching valueP_(k).

The computer 14 calculates the distance between the position (X_(re),Y_(re)) where the optical axis of light illuminating the retina 61 ofthe eye under examination 60 meets the retina 61 and the macular, andselects the types of pattern and pattern template with reference to atable storing the relationship between the calculated distance and thetype of pattern (S601).

FIG. 16 is a view showing the relationship between the distance from themacular and the size of the cell. As shown in the figure, the size ofthe cell at the retina of a human eye depends on the distance from themacular. A pattern of a size corresponding to the distance from themacular is selected through pattern matching in this embodiment.

The computer 14 calculates the distance between (X_(re), Y_(re)) and themacular and obtains a cell size “cs” in accordance with the calculateddistance. A table associating the distance from the macular with thecell size may be stored beforehand in the memory, so that the computer14 can read the cell size “cs” corresponding to the calculated distancefrom the table. Alternatively, an approximate expression of the graphshown in FIG. 16 may be stored in the memory, so that the computer 14can obtain the cell size based on the calculated distance in accordancewith the approximate expression. The computer 14 selects the patternoriginal image Pat(x,y) in accordance with the obtained cell size “cs”.

FIG. 17 is a view illustrating pattern original images. A line sectionof a pattern is assigned a pixel value of 1 and is created with arelatively smaller size than the cell size “cs”. The other section ofthe pattern has a pixel value of 0. A desired number of patterns arecreated in advance, each having a different cell size “cs”, and thepattern original images are stored in the memory in association with therange of the cell size “cs” identifying each pattern. The computer 14can select a pattern corresponding to the obtained cell size “cs” withreference to the range of the cell size “cs” stored in the memory.

FIG. 18 is a view illustrating pattern template images PT(x,y). Alattice image corresponding to the cell size “cs” is created as apattern template image corresponding to the pattern original imagedescribed above. Supposing the line section has a pixel count N1, theinternal shaded section is created to have a pixel count N2 and a pixelvalue of −N1/N2. The pattern template image is stored in the memory inassociation with the pattern described above.

A pattern original image and a pattern template image can have anotherpattern corresponding to the cell size or any other pixel value. Thepattern may not be a square lattice as described above, and a sphericalobject likened as a cell may be used, for instance, as a pattern. Apattern or a pattern template which has already been created and storedin the memory may not be selected, and a pattern may be created, forexample, in accordance with the obtained cell size.

Back to the flow chart shown in FIG. 15, the computer 14 calculates thepupil function f(x,y) from the wavefront aberration W(X,Y) (S603), asexpressed by:f(x,y)=e ^(ikw(X,Y))

(i: Imaginary, k: Wave vector (2π/λ), λ: Wavelength) The computer 14calculates a luminance distribution function Pat(x,y) of the selectedpattern, with reference to the memory (S607). The computer 14 performs atwo-dimensional Fourier transform of Pat(x,y) and obtains a spatialfrequency distribution FPat(u,v) (S609).

The computer 14 obtains the spatial frequency distribution OTF of theeye from the pupil function, and obtains a frequency distributionOR(u,v) (of a retina image) after the passage of the optical system ofthe eye, by multiplying the spatial frequency distribution FPat(u,v) ofthe pattern and the spatial frequency distribution OTF(u,v) of the eye,as expressed below (S611):FPat(u,v)×OTF(u,v)→OR(u,v)

The computer 14 calculates the luminance distribution function PT(x,y)of the pattern template with reference to the memory (S613). Thecomputer 14 obtains a two-dimensional Fourier transform FPT(u,v) ofPT(x,y) (S615).

The computer 14 obtains OTmp(u,v) by multiplying the spatial frequencydistribution OR(u,v) of the retina image calculated from the wavefrontand the spatial frequency distribution FPT(u,v) of the pattern (S617).OR(u,v)×FT(u,v)→OTmp(u,v)The computer 14 then performs a two-dimensional inverse Fouriertransform of OTmp(u,v) to obtain TmpIm(X,Y) (S619). The computer 14obtains the maximum value of the absolute value of TmpIm(X,Y) and usesit as the pattern matching value P_(k) (S621). The computer 14terminates the calculation of the patter matching value and returns tostep S517 shown in FIG. 14.4. Example of Comparison

FIG. 19 is a view comparing an image obtained through patternoptimization with other images. The figure shows a wavefront aberration,a simulated Landolt's ring image, a simulated moire image, and RMS whenno correction is made, when correction is made to decrease theaberration amount RMS (RMS optimization), and when correction is madethrough pattern optimization of this embodiment. The figure indicatesthat the image of pattern optimization can be perceived better althoughpattern optimization provides a greater RMS than RMS optimization.

5. Appendix

The retina observation apparatus and retina observation system of thepresent invention can be provided by an retina observation program forexecuting the processing by a computer, a computer-readable recordingmedium storing the retina observation program, a program product thatcan be loaded into the internal memory of the computer, including theretina observation program, a computer such as a server containing theprogram, or the like.

The optical characteristics measurement block 14-1 obtains the opticalcharacteristics of the eye under examination 60, from the output of thefirst light-receiving optical block 12 shown in FIG. 1. Theconfiguration can be changed to obtain the optical characteristics fromwavefront measurement data including wavefront aberration from anappropriate optical block or apparatus.

INDUSTRIAL APPLICABILITY

According to this invention, it can be adjusted the correction to bemade by the compensating optical device so that the quality of theretina image is improved, and obtained an appropriate amount ofcorrection. According to this invention, it can be obtained anappropriate amount of correction for improving the picture quality inaccordance with a value obtained from pattern matching between themanner in which a visual target is perceived by an eye under examinationand a certain pattern template, or an MTF (modulation transferfunction). Furthermore, according to this invention, it can be providedan retina image corrected by an appropriate correction amount. Accordingto this invention, it can be improved the quality of the retina image bymeans of a voltage-change template provided to adjust the correctionamount of the compensating optical device. According to this invention,it can be evaluated the image quality in consideration of the size ofthe retina cell and to enable observations up to the cell level.

1. An retina observation apparatus comprising: an retina illuminationunit for illuminating the retina of an eye under examination for thepurpose of observation; a compensating optical section for correcting aimage of the retina formed by the illumination of the retinaillumination unit by a given amount of correction; anretina-image-forming optical block for forming an retina image byreceiving the image of the retina corrected by the compensating opticalsection; an retina-image-light-receiving section for receiving theretina image formed by the retina-image-forming optical block; awavefront measurement block for obtaining wavefront measurement dataincluding at least either or both of a wavefront aberration of the eyeunder examination and the aberration corrected by the compensatingoptical section; an optical characteristics measurement block forobtaining optical characteristics including a high-order aberration ofthe eye under examination, from the wavefront measurement data given bythe wavefront measurement block; an image data formation block forsimulating the manner in which a visual target is perceived on theretina, in accordance with the optical characteristics obtained by theoptical characteristics measurement block, and calculating dataindicating the manner of perception; a storage block for storing aplurality of voltage-change templates for use in an adjustment of thecompensating optical section; and a correction amount determinationblock for selecting a voltage-change template stored in the storageblock, determining an amount of correction to be made by thecompensating optical section in accordance with the template andoutputting the amount of correction to the compensating optical section,obtaining evaluation data for evaluating the quality of the image inaccordance with the data indicating the manner in which the visualtarget is perceived, obtained by the image data formation block, inconsideration of the amount of correction based on the plurality ofvoltage-change templates, determining an appropriate amount ofcorrection to be made by the compensating optical section in accordancewith the evaluation data, and outputting the appropriate amount ofcorrection to the compensating optical section.
 2. An retina observationapparatus according to claim 1, wherein the compensating optical sectionincludes adaptive optics having a plurality of movable mirrors orspatial optical modulators.
 3. An retina observation apparatus accordingto claim 2, wherein the compensating optical section further includeseither or both of a moving prism configured to be capable of moving inthe direction of the optical axis and a spherical lens section.
 4. Anretina observation apparatus according to claim 1, wherein the wavefrontmeasurement block comprises: a point-image-projecting optical block forprojecting a point image onto the retina of the eye under examination; apoint-image-light-receiving optical block for forming a point imagethrough a splitting element for splitting a light beam sent by thepoint-image-projecting optical block and reflected by the retina of theeye under examination into at least seventeen light beams; and apoint-image-light-receiving section for receiving the point image formedby the point-image-light-receiving optical block; and the opticalcharacteristics measurement block is configured to obtain the outputfrom the point-image-light-receiving section as the wavefrontmeasurement data and determine the optical characteristics including thehigh-order aberration of the eye under examination.
 5. An retinaobservation apparatus according to claim 1, wherein the voltage-changetemplates stored in the storage block include one or more of aconcentric template having a greater voltage change specified near thecenter of the compensating optical section than in the periphery, asymmetric template having voltage changes specified symmetrically withrespect to the center or a desired axis of the compensating opticalsection, and an asymmetric template having voltage changes specifiedasymmetrically with respect to the center or a desired axis of thecompensating optical section.
 6. An retina observation apparatusaccording to claim 5, wherein the correction amount determination blockselects a concentric template if an amount of spherical aberrationexceeds a certain level, selects a symmetric template if an astigmaticcomponent exceeds a certain level, or selects an asymmetric template ifa coma-like aberration component exceeds a certain level, in accordancewith the amount of aberration obtained by the optical characteristicsmeasurement block.
 7. An retina observation apparatus according to claim1, wherein the image data formation block simulates the manner in whicha certain visual target is perceived on the retina and obtains simulatedimage data; and the correction amount determination block is configuredto compare pattern template data corresponding to the visual target andthe simulated image data through pattern matching and determine anappropriate amount of correction in accordance with a value indicatingthe degree of matching.
 8. An retina observation apparatus according toclaim 7, wherein the correction amount determination block is configuredto perform a two-dimensional Fourier transform of a luminancedistribution function of the pattern template data corresponding to thevisual target used for simulation, carry out pattern matching bymultiplying the result of the Fourier transform by the spatial frequencydistribution of the simulated image data, and determine whether thecorrection amount is appropriate in accordance with a value indicatingthe degree of matching.
 9. An retina observation apparatus according toclaim 8, wherein the image data formation block is configured tocalculate a spatial frequency distribution of the eye in accordance withthe wavefront aberration, perform a two-dimensional Fourier transform ofa luminance distribution function of a certain visual target, and obtainthe spatial frequency distribution of simulated image data bymultiplying the spatial frequency distribution of the eye by the resultof the Fourier transform.
 10. An retina observation apparatus accordingto claim 7, wherein the image data formation block is configured tocalculate the distance between a point where the optical axis of lightilluminating the retina of the eye under examination meets the retinaand a macular, and use a visual target corresponding to the calculateddistance.
 11. An retina observation apparatus according to claim 1,wherein the image data formation block calculates MTF (modulationtransfer function) data as data indicating the manner of perception of aimage, in accordance with the optical characteristics obtained by theoptical characteristics measurement block; and the correction amountdetermination block is configured to determine an appropriate amount ofcorrection in accordance with the calculated MTF data.
 12. An retinameasurement apparatus according to claim 11, wherein the correctionamount determination block calculates the distance between a point wherethe optical axis of light illuminating the retina of the eye underexamination meets the retina and a macular, obtains a spatial frequencycorresponding to the calculated distance, with reference to dataindicating the relationship between the distance from the macular andthe spatial frequency, stored beforehand in the storage block,calculates an MTF value corresponding to the spatial frequency, on thebasis of the obtained spatial frequency and the MTF data calculated bythe image data formation block, and determines an appropriate amount ofcorrection in accordance with the MTF value.
 13. An retina observationapparatus according to claim 1, wherein the correction amountdetermination block determines an amount of correction to startcorrection from weak correction side.
 14. An retina observation methodcomprising: a step of illuminating the retina of an eye underexamination for the purpose of observation; a step of correcting a imageof the retina formed by the illumination, by a given amount ofcorrection; a step of forming an retina image by receiving the correctedimage of the retina; a step of measuring wavefront measurement dataindicating at least either or both of a wavefront aberration of the eyeunder examination and the aberration to be corrected; a step ofobtaining optical characteristics including a high-order aberration ofthe eye under examination, from the wavefront measurement data; a stepof calculating data indicating the manner of perception, by simulatingthe manner in which a image is perceived on the retina, in accordancewith the obtained optical characteristics; a step of determining andoutputting the amount of correction in accordance with the templatewhich is selected a voltage-change template for use in an adjustment ofan amount of correction and; a step of determining an appropriate amountof correction in accordance with the evaluation data which is obtainedfor evaluating the quality of the image in accordance with the dataindicating the manner in which the image is perceived, in considerationof the amount of correction based on a plurality of voltage-changetemplates and a step of outputting the amount of correction determinedin the step of determing.
 15. An retina observation method according toclaim 14, wherein a correction is made by adaptive optics having aplurality of movable mirrors or spatial optical modulators, in the stepof correcting.
 16. An retina observation method according to claim 15,wherein a further correction is made by both or either of a moving prismconfigured to be capable of moving in the direction of the optical axisand a spherical lens section, in the step of correcting.
 17. An retinaobservation method according to claim 14, wherein the step of measuringcomprises steps of: projecting a point image onto the retina of the eyeunder examination; forming a point image through a splitting element forsplitting a light beam reflected by the retina of the eye underexamination into at least seventeen light beams; and receiving theformed point image; and the received point image data is obtained as thewavefront measurement data indicating at least a wavefront aberration ofthe eye under examination, and the optical characteristics including thehigh-order aberration of the eye under examination are obtained, in thestep of determinating.
 18. An retina observation method according toclaim 14, wherein a voltage-change template to be selected in the stepof outputting is one or more of a concentric template having a greatervoltage change specified near the center of the compensating opticalsection for correcting the image of the retina than in the periphery, asymmetric template having voltage changes specified symmetrically withrespect to the center or a desired axis of the compensating opticalsection, and an asymmetric template having voltage changes specifiedasymmetrically with respect to the center or a desired axis of thecompensating optical section.
 19. An retina observation method accordingto claim 18, wherein a template to be selected in accordance with thecalculated amount of aberration in the step of outputting is aconcentric template if an amount of spherical aberration exceeds acertain level, a symmetric template if an astigmatic component exceeds acertain level, or an asymmetric template if a coma-like aberrationcomponent exceeds a certain level.
 20. An retina observation methodaccording to claim 14, wherein the manner in which a certain visualtarget is perceived on the retina is simulated, and simulated image datais obtained in the step of calculating; and the step of determingcomprises steps of: comparing pattern template data corresponding to thevisual target and the simulated image data through pattern matching; andjudging whether the amount of correction is appropriate, from the valueindicating the degree of matching.
 21. An retina observation methodaccording to claim 20, wherein a two-dimensional Fourier transform isperformed on a luminance distribution function of the pattern templatedata corresponding to the visual target used for simulation, patternmatching is carried out by multiplying the result of the Fouriertransform by the spatial frequency distribution of the simulated imagedata, and whether the correction amount is appropriate is judged fromthe value indicating the degree of matching, in the step of determing.22. An retina observation method according to claim 21, wherein aspatial frequency distribution of the eye is calculated in accordancewith the wavefront aberration, a two-dimensional Fourier transform isperformed on a luminance distribution function of a certain visualtarget, and the spatial frequency distribution of simulated image datais obtained by multiplying the spatial frequency distribution of the eyeby the result of the Fourier transform, in the step of calculating. 23.An retina observation method according to claim 20, wherein the distancebetween a point where the optical axis of light illuminating the retinaof the eye under examination meets the retina and a macular iscalculated, and a visual target corresponding to the calculated distanceis used to simulate the manner of perception, in the step ofcalculating.
 24. An retina observation method according to claim 14,wherein MTF (modulation transfer function) data is calculated as dataindicating the manner of perception of a image in accordance with theobtained optical characteristics in the step of calculating; and anappropriate amount of correction is determined in accordance with thecalculated MTF data in the step of determing.
 25. An retina measurementmethod according to claim 24, wherein the distance between a point wherethe optical axis of light illuminating the retina of the eye underexamination meets the retina and a macular is calculated, a spatialfrequency corresponding to the calculated distance is obtained withreference to data indicating the relationship between the distance fromthe macular and the spatial frequency, stored beforehand in the storageblock, an MTF value corresponding to the spatial frequency is calculatedon the basis of the obtained spatial frequency and the MTF datacalculated by the image data formation block, and an appropriate amountof correction is determined in accordance with the MTF value, in thestep of determing.
 26. An retina observation method according to claim14, wherein an amount of correction is determined to start correctionfrom weak correction side, in the second step of outputting.